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Arithmetic Progressions
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01/06/2021 12:05 pm
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Find the sum of first 51 terms of an AP whose second and third terms are 14 and 18 respectively.
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01/06/2021 12:06 pm
Given that,
Second term, a2 = 14
Third term, a3 = 18
Common difference, d = a3−a2
= 18−14 = 4
a2 = a+d
14 = a+4
a = 10 = First term
Sum of n terms;
Sn = n/2 [2a + (n – 1)d]
S51 = 51/2 [2×10 (51-1) 4]
= 51/2 [2+(20)×4]
= 51 × 220/2
= 51 × 110
= 5610